Pickling



C. J. RODMAN Feb. 7, 1956 PICKLING Filed NOV. 27, 1951 904 OEOm wmz E mmz E umzE umZE

INVENTOR. CLARENCE J. RODMAN g (RM ATTORNEY United States Patent PICKLING Clarence J. Rodman, Alliance, Ohio, assignor, by mesne assignments, to Alliance Ware, Inc., a corporation of Delaware Application November 27, 1951, Serial No. 258,382} 2 Claims. (Cl. 117-50) This invention relates to a process of pickling and coating iron sheet products with a thin coating of an electropositive metal, prior to enameling.

Enameled sheet metal products are manufactured by enameling sheets of high grade iron which have been shaped as desired. It has been customary to pickle the shaped sheets by dipping them in a pickling bath. The operation has been carried out as a batch operation. The pickling operation has sometimes been followed by a nickel or copper dip. This, too, has been carried on as a batch operation.

According to this invention the sheet metal products are both pickled and coated with the electropositive metal in the same bath. The operation is carried out as a continuous process and the conveyor which carries the sheet metal products through the treating bath supplies the electropositive metal for the coating.

The nature of the pickling operation will depend upon the condition of the metal. Thus, if the metal is free from all oil and grease an acid bath may be all that is required. If the metal has been coated with oil or grease or a like material before being drawn or otherwise shaped, it will be desirable to first treat the metal with a detergent before treating with the acid. After leaving the acid bath the acid which adheres to the products is neutralized as a part of the continuous process.

Any suitable conveyor may be used to carry the shaped sheets through the treating baths. A plurality of cables of Monel metal or other so-called acid-resistant metal has been found satisfactory. The process is particularly applicable to the treatment of larger products such as table tops, bathtubs, refrigerator boxes, shower baths, lavatories, etc. These are preferably placed on the cables or other conveyor means so that they make only point contact therewith, to cause minimum or no interference with the pickling and coating.

The baths are preferably sprayed against the sheet metal products. The sprays may be set at different angles to insure treatment of all surfaces of the products. The baths are preferably hot, for example 20 to 30 F. below their boiling point. They heat the sheet during the treatment, so that after all the spray has been completed the products are hot enough to cause rapid evaporation of any liquid adhering to their surface.

Any suitable detergent may be used to remove all grease and oil. Aqueous soaps, alkalis, etc. can be used. After the detergent treatment the metal is thoroughly rinsed with Water.

Dilute acid, such as sulfuric acid or hydrochloric acid, etc., is employed for pickling. An aqueous solution of 6 to 12 or perhaps 15 percent or higher of hydrochloric acid has been found entirely satisfactory. After pickling, the shaped sheets are thoroughly rinsed. They are then preferably passed through a neutralizer such as aqueous boric acid, etc. There is no need for removing boric acid prior to enameling.

The electropositive metal is supplied to the acid bath 2,733,999 Patented Feb. 7, 1956 by solution from the conveyor. The conveyor may, for example, be Monel metal which contains 60 or more per cent nickel and 25 to 35 per cent of copper. The balance may be iron and may include other metals, such as manganese, silicon and carbon. If the formed sheets are to be carried on cables, the Monel metal recommended for cables will be employed. Other carriers than cables may be utilized. Likewise other highly acid resistant alloys which contain a metal electropositive to iron may be used. In the hot acid bath there is some solution ofthe Monel metal or other metal. It produces a very low concentration of the electropositive metal in the bath. If Monel is employed the acid bath will contain a very low percentage of both nickel and copper. When thevbath contacts the iron products an exceedingly thin but uniform coating of the metal electropositive to the iron is formed on their surface.

The invention will be further described in connection with the accompanying drawings, in which- Fig. 1 is a plan view of a preferred form of equipment; and

Fig. 2 is a section therethrough.

The drawings are quite schematic. The spray devices are illustrative only, and in practice there will be many sprays, and the sprays for any of the treatments will be arranged to treat the entire surface of any sheet product passed through them.

The cables 1 are of Monel metal. They are supported on the two drums 2 and intermediate these drums are many idlers (not shown) which maintain the upper stretch of the cables in a horizontal plane. Drive means (not shown) is provided.

The sheet is first subjected to a hot alkali bath. This may, for example, be a 10 to 20 per cent aqueous solution of sodium hydroxide. It will remove all oily and saponifiable materials. Each of the baths is composed of a hood 5 and a pan 6 which collects the used spray. This is recirculated by means of a pump (not shown) and the bath is re-sprayed through the upper sprays 8 and lower sprays 9. The temperature of the sprays is advantageously controlled by thermostatic means (not shown). Means is provided for supplying additional treating liquid to each bath continuously or in increments. It may be necessary to draw off some used alkali continuously or in increments and replace it with fresh material. It will be necessary to remove some of the used liquid from the rinse baths. Generally it will not be necessary to draw off any of the acid bath because the sheet is clean. Some acid will be consumed in attacking the cables and some will be lost by adherence to the sheet. The amount of iron salt which is formed will be small and its concentration in the bath will be kept low by the constant removal of some acid which adheres to the sheet, and replenishment of the bath by addition of fresh acid.

After the alkali treatment the sheet is thoroughly rinsed with hot water. It is then passed through the hot aqueous acid sprays. The acid attacks the Monel metal but only slightly. The amount the metal is attacked depends upon the concentration and temperature of the acid and the amount of spray which contacts the metal. The coating of the electropositive metal is so very thin that the same process can be used for both large and small objects. In one operation, twenty-one minutes are consumed in conveying the sheet products feet from the drum at one end of the system to the drum at the other end. The coating of copper and nickel on the sheet approaches molecular thickness. By changing the strength of the acid, the width of the acid bath, the speed at which the cables are traveling, and the temit perature of the bath, the thickness of the 'copper and nickel coat may be varied.

After the acid treatment the products are thoroughly rinsed with hot water. Any neutralizer may be employed. Hot, weak aqueous boric acid is preferred because after it is used the products need not be subjected to a subsequent rinse. After the neutralizer treatment the products pass through a drying tunnel. Here the heat of the products is sufiicient to vaporize all of the water which adheres to them. The products then pass out of the tunnel on the cables. If the top of a product is formed with indentations so that it is not self-draining, any liquid that has collected on it is dumped and caught in the drain 12. The products are still so Warm that the moisture which adheres after such dumping is quickly evaporated.

The equipment is provided with vents (not shown) to carry off the steam from the drier and elsewhere, if required. Fans are used to maintain the required circulation.

What I claim is:

1. The process of pickling iron objects supported on a conveyor of highly acid-resistant metal electropositive to the iron and composed essentially of copper and nickel, which comprises continually moving the objects while supported upon the conveyor through a series of sprays each of which continuously sprays the conveyor and the entire surface of each of the objects in succession as it is moved through the spray, said sprays including (1) a spray which removes oil and grease from the objects,

(2) pickling spray of dilute acid heated to a temperature at which the conveyor is attacked, but only slightly, to produce a solution of low concentration of electropositive metal in the liquid resulting from the spraying operation, using said liquid for spraying additional objects whereby metal dissolved from the conveyor is deposited on the objects, and (3) spray to remove the acid, each of said sprays being heated whereby the objects after final spraying are heated sufliciently to dry substantially more rapidly than if unheated, and moving the conveyor at such a rate that only a very thin deposit of the metal is formed on the objects.

2. The process of the preceding claim in which the pickling spray is sulfuric acid heated to a temperature of no less than 30 F. below its boiling point.

References Cited in the file of this patent UNITED STATES PATENTS 1,165,338 Moench Dec. 21, 1917 1,430,054 Camelo Sept. 26, 1922 1,627,096 Jones et al May 3, 1927 1,656,528 Mallard Jan. 17, 1928 1,679,435 McFetridge Aug. 7, 1928 2,570,299 Zademach et al. Oct. 9, 1951 OTHER REFERENCES Sivitz: Metal Cleaning and Finishing, vol. 6, pp. 73-5. Hedges: Protective Films on Metals, 2nd col. pg. 235, lines 28-31, pg. 236, lines 6-9. 

1. THE POCESS OF PICKLING IRON OBJECTS SUPPORTED ON A CONVEYOR OF HIGHLY ACID-RESISTANT METAL ELECTROPOSITIVE TO THE IRON AND COMPOSED ESSENTIALLY OF COPPER AND NICKEL, WHICH COMPRISES CONTINUALLY MOVING TEH OBJECTS WHILE SUPPORTED UPON THE CONVEYOR THROUGH A SERIES OF SPRAYS EACH OF WHICH CONTINUOUSLY SPRAYS THE CONVEYOR AND THE ENTIRE SURFACE OF EACH OF THE OBJECTS IN SUCCESSION AS IT IS MOVED THROUGH THE SPRAY, SAID SPRAYS INCLUDING (1) A SPRAY WHICH REMOVES OIL AND GREASE FROM THE OBJECTS, (2) PICKING SPRAY OF DILUTE ACID HEATED TO A TEMPERATURE AT WHICH THE CONVEYOR IS ATTACKED, BUT ONLY SLIGHTLY, TO PRODUCE A SOLUTION OF LOW CONCENTRATION OF ELECTROPOSITIVE METAL IN THE LIQUID RESULTING FROM THE SPRAYIN OPERATION, USING SAID LIQUID FOR SPRAYING ADDITIONAL OBJECTS WHEREBY METAL DISSOLVED FROM THE CONVEYOR IS DEPOSITED ON THE OBJECTS, AND (3) SPRAY TO REMOVE THE ACID, EACH OF SAID SPRAYS BEING HEATED WHEREBY THE OBJECTS AFTER FINAL SPRAYING ARE HEATED SUFFICIENTLY TO DRY SUBSTANTIALLY MORE RAPIDLY THAN IF UNHEATED, AND MOVING THE CONVEYOR AT SUCH A RATE THAT ONLY A VERY THIN DEPOSIT OF THE METAL IS FORMED ON THE OBJECTS. 